U.S. patent application number 13/353208 was filed with the patent office on 2013-07-18 for system for deaeration in a flash vessel.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is Rupinder Singh Benipal, Vishal Rugnathbhai Brahmbhatt, George Morris Gulko, Srikanth Konda, John Saunders Stevenson. Invention is credited to Rupinder Singh Benipal, Vishal Rugnathbhai Brahmbhatt, George Morris Gulko, Srikanth Konda, John Saunders Stevenson.
Application Number | 20130183204 13/353208 |
Document ID | / |
Family ID | 47563250 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130183204 |
Kind Code |
A1 |
Benipal; Rupinder Singh ; et
al. |
July 18, 2013 |
SYSTEM FOR DEAERATION IN A FLASH VESSEL
Abstract
The disclosed embodiments relate to systems for deaerating a
stream of slag sump water produced by a gasifier. For example, in
one embodiment, a system includes a flash vessel having a first
inlet configured to introduce a first fluid into the flash vessel,
wherein the flash vessel is configured to flash the first fluid to
produce a first flash gas, a second inlet configured to introduce a
stream from slag sump into the flash vessel, wherein the stream
from slag sump comprises a mixture of a gasification fine slag,
dissolved oxygen (O.sub.2), and water. A gas-liquid contactor in
the flash vessel is configured to contact the stream from slag sump
with the first flash gas to enable the first flash gas to deaerate
the stream from slag sump. A first outlet of the vessel is
configured to output an overhead discharge comprising the first
flash gas and oxygen from the stream from slag sump.
Inventors: |
Benipal; Rupinder Singh;
(Houston, TX) ; Gulko; George Morris; (Houston,
TX) ; Stevenson; John Saunders; (Yorba Linda, CA)
; Konda; Srikanth; (Bangalore, IN) ; Brahmbhatt;
Vishal Rugnathbhai; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Benipal; Rupinder Singh
Gulko; George Morris
Stevenson; John Saunders
Konda; Srikanth
Brahmbhatt; Vishal Rugnathbhai |
Houston
Houston
Yorba Linda
Bangalore
Houston |
TX
TX
CA
TX |
US
US
US
IN
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
47563250 |
Appl. No.: |
13/353208 |
Filed: |
January 18, 2012 |
Current U.S.
Class: |
422/187 ;
422/310 |
Current CPC
Class: |
C02F 2103/365 20130101;
B01D 3/06 20130101; C10J 2300/0906 20130101; B01D 3/065 20130101;
C10J 3/84 20130101; C10J 2300/0946 20130101; C10J 2300/093
20130101; C02F 1/20 20130101; C02F 2103/18 20130101; C10J 3/723
20130101; C10J 2300/0976 20130101; C10J 2300/169 20130101; B01D
19/0036 20130101; C10J 2300/0959 20130101; Y02E 20/18 20130101;
C10J 3/526 20130101; C10J 2300/0916 20130101; Y02E 20/16
20130101 |
Class at
Publication: |
422/187 ;
422/310 |
International
Class: |
B01J 7/00 20060101
B01J007/00; B01J 19/30 20060101 B01J019/30 |
Claims
1. A system, comprising: a flash vessel comprising: a first inlet
configured to introduce a first fluid into the flash vessel,
wherein the flash vessel is configured to flash the first fluid to
produce a first flash gas; a second inlet configured to introduce a
stream of slag sump water into the flash vessel, wherein the stream
of slag sump water comprises a mixture of water, oxygen (O.sub.2),
and at least one of a gasification slag and char; a gas-liquid
contactor disposed within the flash vessel, wherein the gas-liquid
contactor is configured to contact the stream of slag sump water
with the first flash gas to enable the first flash gas to deaerate
the stream of slag sump water; and a first outlet configured to
output an overhead discharge comprising a second flash gas and
oxygen from the stream of slag sump water.
2. The system of claim 1, wherein the gas-liquid contactor is
positioned within the flash vessel between the first inlet and the
second inlet, and wherein the second inlet is disposed above the
first inlet.
3. The system of claim 2, wherein the first outlet is disposed
above the second inlet, the flash vessel comprises a second outlet
disposed below the first inlet, and the second outlet is configured
to output a stream of substantially deaerated liquid.
4. The system of claim 2, wherein the flash vessel comprises a
third inlet disposed below the second inlet, the third inlet is
configured to receive steam, and the steam is used in addition to
the first flash gas to deaerate the stream of slag sump water.
5. The system of claim 1, wherein the gas-liquid contactor
comprises a fixed valve tray, a packed bed having a plurality of
Raschig rings, a sieve tray, or a combination thereof.
6. The system of claim 1, comprising: a gasifier fluidly coupled to
the first inlet of the flash vessel, comprising: a gasification
vessel configured to receive and gasify a carbonaceous fuel to
produce a first syngas mixture; and a quench portion configured to
contact the first syngas mixture with water to produce a quenched
syngas stream, a slag stream, and a blackwater stream, and wherein
the first fluid comprises the blackwater stream.
7. The system of claim 6, wherein the blackwater stream has a
pressure of between approximately 10 and 85 bar.
8. The system of claim 6, wherein the flash vessel has an average
pressure of between approximately 2 and 10 bar.
9. The system of claim 1, wherein the flash vessel comprises a
third inlet configured to receive a liquid feed, and the gas-liquid
contactor is configured to contact the liquid feed with the first
flash gas to enable the first flash gas to deaerate liquid feed,
and wherein the liquid feed comprises process water produced within
a gasification system, or a stream of fines filtrate produced
within the gasification system, or a combination thereof.
10. A system, comprising a gasifier configured to gasify a
carbonaceous feed to produce syngas; a quench portion configured to
quench the produced syngas using at least water to generate a
stream of quenched syngas, a slag stream having dissolved oxygen,
and a blackwater stream; a flash vessel disposed downstream from
the quench portion, wherein the flash vessel is configured to
receive a liquid feed at a first inlet and the blackwater stream at
a second inlet, wherein the liquid feed comprises a stream of slag
sump water generated by water contact with the slag stream, and
wherein the flash vessel comprises a gas-liquid contactor
configured to contact the liquid feed with a first flash gas to
deaerate the slag sump water to produce a stream of substantially
deaerated liquid.
11. The system of claim 10, wherein the first flash gas comprises
steam produced from the blackwater stream.
12. The system of claim 11, wherein the flash vessel is at a first
pressure and the blackwater stream is at a second pressure, the
first pressure is lower than the second pressure, and the flash
vessel is configured to flash at least the steam contained within
the blackwater stream.
13. The system of claim 12, wherein the second pressure is between
approximately 10 and 85 bar, and the first pressure is between
approximately 2 and 10 bar.
14. The system of claim 11, wherein the first inlet is disposed
above the second inlet, and the gas-liquid contactor is positioned
within the flash vessel between the first inlet and the second
inlet.
15. The system of claim 14, wherein the gas-liquid contactor
comprises a plurality of flow impeding structures configured to
increase contact of the liquid feed with the first flash gas in a
counterflow of the liquid feed against the first flash gas.
16. The system of claim 15, wherein the plurality of flow impeding
structures comprises a fixed valve tray, a packed bed having a
plurality of Raschig rings, a sieve tray, or a combination
thereof.
17. The system of claim 10, comprising a slag sump disposed
downstream from the quench portion, wherein the slag sump is
configured to receive at least a portion of the slag stream from
the quench portion, and the slag sump is configured to generate the
stream of slag sump water.
18. The system of claim 17, comprising: a settler disposed
downstream from the flash vessel, wherein the settler is configured
to separate the stream of substantially deaerated liquid into a
stream of grey water and a stream of fines; and a filter disposed
downstream from the settler, wherein the filter is configured to
separate the stream of fines into a filter cake and a filtrate
stream comprising water and dissolved gases, the filter is coupled
to the slag sump, the second flash vessel, or both, and the slag
sump, the second flash vessel, or both, are configured to receive
the filtrate stream such that the liquid feed comprises at least a
portion of the filtrate stream.
19. A system, comprising: a gasifier configured to gasify a
carbonaceous feed to produce a syngas; a quench portion configured
to quench the syngas using at least water to generate a stream of
quenched syngas, a slag stream, and a first blackwater stream; a
first flash vessel disposed downstream from the quench portion,
wherein the first flash vessel is configured to receive and flash
the first blackwater stream at a first pressure to produce a first
flash gas and a second blackwater stream, and the second blackwater
stream has a lower pressure than the first blackwater stream; and a
second flash vessel disposed downstream from the first flash
vessel, wherein the second flash vessel is configured to receive
the second blackwater stream at a first inlet, the second flash
vessel is configured to receive a liquid feed having dissolved
oxygen at a second inlet, and the second flash vessel is configured
to flash the second blackwater stream at a second pressure to
produce a second flash gas to deaerate the liquid feed to produce a
stream of substantially deaerated liquid.
20. The system of claim 19, wherein the second flash vessel
comprises a gas-liquid contactor, and the gas-liquid contactor
comprises a plurality of flow impeding structures configured to
increase contact of the liquid feed with the second flash gas in a
counterflow of the stream of slag sump water against the second
flash gas.
21. The system of claim 19, comprising a slag sump disposed
downstream from the quench portion, wherein the slag sump is
configured to receive at least a portion of the slag stream from
the quench portion, the slag sump is configured to remove a portion
of water within the slag stream to generate a stream of slag sump
water and a water recycle stream, the water recycle stream is
recycled to the gasifier, and the liquid feed comprises the stream
of slag sump water.
22. The system of claim 21, comprising: a settler disposed
downstream from the second flash vessel, wherein the settler is
configured to separate the stream of substantially deaerated liquid
into a stream of grey water and a stream of fines; and a filter
disposed downstream from the settler, wherein the filter is
configured to separate the stream of fines into a filter cake and a
filtrate stream comprising water and dissolved gases, the filter is
coupled to the slag sump, the second flash vessel, or both, and the
slag sump, the second flash vessel, or both, are configured to
receive the filtrate stream such that the liquid feed comprises at
least a portion of the filtrate stream.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to syngas
production systems and, more particularly, to systems for the
deaeration of stream of slag sump water produced by a gasifier.
[0002] Gasifiers convert carbonaceous materials into a mixture of
carbon monoxide and hydrogen, referred to as synthesis gas or
syngas. For example, an integrated gasification combined cycle
(IGCC) power plant includes one or more gasifiers that react,
through a series of reactions, a feedstock at a high temperature
with oxygen and/or steam to produce syngas. The series of reactions
is collectively referred to as the gasification process. Upon
gasification, the resulting syngas may include less desirable
component, such as hot ash in the form of slag. Accordingly, the
syngas may be directed through a quench unit to cool the syngas to
a saturation temperature and remove at least some of the less
desirable components. The less desirable components may form
by-products, such as a slag stream produced from the ash.
BRIEF DESCRIPTION OF THE INVENTION
[0003] Certain embodiments commensurate in scope with the
originally claimed invention are summarized below. These
embodiments are not intended to limit the scope of the claimed
invention, but rather these embodiments are intended only to
provide a brief summary of possible forms of the invention. Indeed,
the invention may encompass a variety of forms that may be similar
to or different from the embodiments set forth below.
[0004] In a first embodiment, a system includes a flash vessel
having a first inlet configured to introduce a first fluid into the
flash vessel, wherein the flash vessel is configured to flash the
first fluid to produce a first flash gas, a second inlet configured
to introduce a stream of slag sump water into the flash vessel,
wherein the stream of slag sump water includes a mixture of water,
oxygen (O.sub.2), and at least one of a gasification slag and char,
a gas-liquid contactor disposed within the flash vessel, wherein
the gas-liquid contactor is configured to contact the stream of
slag sump water with the first flash gas to enable the first flash
gas to deaerate the stream of slag sump water; and a first outlet
configured to output an overhead discharge having a second flash
gas and oxygen from the stream of slag sump water.
[0005] In a second embodiment, a system includes a gasifier
configured to gasify a carbonaceous feed to produce syngas, a
quench portion configured to quench the produced syngas using at
least water to generate a stream of quenched syngas, a slag stream
having dissolved oxygen, and a blackwater stream. The system also
includes a flash vessel disposed downstream from the quench
portion, wherein the flash vessel is configured to receive a liquid
feed at a first inlet and the blackwater stream at a second inlet,
wherein the liquid feed comprises a stream of slag sump water
generated by water contact with the slag stream, and wherein the
flash vessel comprises a gas-liquid contactor configured to contact
the liquid feed with a first flash gas to deaerate the slag sump
water to produce a stream of substantially deaerated liquid
feed.
[0006] In a third embodiment, a system includes a gasifier
configured to gasify a carbonaceous feed to produce a syngas, a
quench portion configured to quench the syngas using at least water
to generate a stream of quenched syngas, a slag stream, and a first
blackwater stream. The system also includes a first flash vessel
disposed downstream from the quench portion, wherein the first
flash vessel is configured to receive and flash the first
blackwater stream at a first pressure to produce a first flash gas
and a second blackwater stream, and the second blackwater stream
has a lower pressure than the first blackwater stream. The system
further includes a second flash vessel disposed downstream from the
first flash vessel, wherein the second flash vessel is configured
to receive the second blackwater stream at a first inlet, the
second flash vessel is configured to receive a liquid feed having
dissolved oxygen at a second inlet, and the second flash vessel is
configured to flash the second blackwater stream at a second
pressure to produce a second flash gas to deaerate the liquid feed
to produce a stream of substantially deaerated liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0008] FIG. 1 is a diagrammatical illustration of an embodiment of
a gasification system configured to produce syngas and to process
black water and a stream of slag sump water produced by the system,
the system including a high pressure flash tank configured to
reduce a pressure of the black water and a low-pressure flash tank
configured to further reduce a pressure of the black water and
deaerate the stream of slag sump water using the black water;
[0009] FIG. 2 is a diagrammatical illustration of an embodiment of
a gasification system configured to produce syngas and to process
black water and a stream of slag sump water produced by the system,
the system including a low-pressure flash tank configured to
receive the black water directly from a gasifier of the system and
deaerate the slag sump using the black water flash gas;
[0010] FIG. 3 is a diagrammatical illustration of a generalized
embodiment of the low-pressure flash tank of FIG. 1 or 2;
[0011] FIG. 4 is a diagrammatical illustration of an embodiment of
the low-pressure flash tank of FIG. 3 using a plurality of fixed
valve trays as the gas-liquid contactor; and
[0012] FIG. 5 is a diagrammatical illustration of an embodiment of
the low-pressure flash tank of FIG. 3 using a fixed bed formed from
a plurality of Raschig rings as the gas-liquid contactor.
DETAILED DESCRIPTION OF THE INVENTION
[0013] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, all features of an actual
implementation may not be described in the specification. It should
be appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0014] When introducing elements of various embodiments of the
present invention, the articles "a," "an," "the," and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements.
[0015] As noted above, gasifiers that produce syngas may also
produce by-products, such as slag. The slag from the gasifier is
mixed with water in a quench, and flows out of the quench as a slag
stream. The slag stream is depressurized and collected in a slag
sump. The slag stream is removed from the slag sump and dewatered,
making the recovered water and water in the slag sump available for
further use. Unfortunately, the water recovered from the slag
stream and in the slag sump also includes dissolved oxygen absorbed
from the air, such as the air in the immediate vicinity of slag
sump 40, which can corrode various features disposed downstream
from the gasifier. The downstream components may include piping,
conduits, vessels, heat exchangers and/or pumps. In certain
configurations, the oxygen may be removed using a vacuum flash
vessel. The vacuum flash vessel uses vacuum pumps and associated
equipment to enable the pressure within the vessel to be reduced
below atmospheric pressure, or below the lowest operational
pressure of a plant system having the gasifier. Accordingly,
typical approaches toward the removal of dissolved oxygen in slag
streams are often inefficient, costly, and/or subject to further
improvement.
[0016] The present embodiments overcome these and other
shortcomings by providing a low-pressure flash vessel having one or
more gas-liquid contactors. The flash vessel is configured such
that an aerated liquid feed, such as a stream of slag sump water
having dissolved oxygen, flows over and through the gas-liquid
contactor. Additionally, a flash gas, such as steam evolved from a
gasifier blowdown stream as a result of a pressure reduction, flows
through the gas-liquid contactor. The flash gas and the aerated
liquid feed contact one another at the gas-liquid contactor, and
the flash gas removes at least a portion of the dissolved oxygen in
the liquid feed. In other words, the gasifier blowdown stream may
be used to deaerate the stream of slag sump water using a single
vessel.
[0017] The present embodiments may be used in conjunction with any
gasification system that produces slag. For example, the present
embodiments may be used in IGCC systems, syngas production systems,
and methanation systems. FIG. 1 illustrates an embodiment of a
gasification system 10. Within the gasification system 10, a
carbonaceous fuel source 12 may be utilized as a source of energy
to produce syngas. The fuel source 12 may include coal, petroleum
coke, biomass, wood-based materials, agricultural wastes, tars, and
asphalt, or other carbon containing materials.
[0018] The fuel source 12 may be introduced into the gasification
system 10 via a feedstock preparation system 14. The feedstock
preparation system 14 may resize or reshape, select, and/or dry the
fuel source 12. According to certain embodiments, the feedstock
preparation system 14 may include a grinding mill. Further, within
the feedstock preparation system 14, additives 16, such as water,
or other suitable liquids, may be added to the fuel source 12 to
create a fuel slurry 18 as a gasifier feed. However, in other
embodiments, such as where no liquid additives are employed, the
gasifier feed 18 may be a dry or partially dried feedstock that may
be conveyed into the gasifier for example using a carrier gas.
[0019] The fuel slurry 18 is directed to a gasifier 20 where the
fuel slurry 18 is mixed with oxygen (O.sub.2) 22 to produce syngas
via a series of reactions, collectively referred to as a
gasification process. In particular, during the gasification
process the fuel slurry 18 may be reacted with a limited amount of
oxygen at elevated pressures (e.g. from absolute pressures of
approximately 20 bar to 85 bar) and temperatures (e.g.,
approximately 700.degree. C. to 1600.degree. C.) to partially
oxidize the fuel slurry 18 and produce syngas. Due to chemical
reactions between the oxygen 22, and the carbon and water within
the fuel slurry 18, the syngas may include hydrogen, carbon
monoxide, and carbon dioxide. Other less desirable components may
also be formed, including products from ash produced during
gasification, sulfur, nitrogen, and chloride.
[0020] The gasifier 20, shown in FIG. 1 as contained within a
single pressure vessel 20 together with quench 26, also referred to
as a quench gasifier, includes a reaction portion 24 where the
gasification process is performed, and a quench portion 26 where
the syngas produced by the gasification process is cooled. Within
the reaction portion 24, the fuel slurry 18 may be heated to
undergo a pyrolysis process. According to certain embodiments,
temperatures inside the gasifier 20 may range from approximately
150.degree. C. to 1600.degree. C. during the pyrolysis process,
depending on the type of fuel source 12 utilized to generate the
fuel slurry 18. The heating of the feedstock during the pyrolysis
process may generate a solid, e.g., char, and residue gases, e.g.,
carbon monoxide and hydrogen.
[0021] A combustion process may then occur in the gasifier 20. The
combustion may include introducing oxygen to the char and residue
gases. The char and residue gases may react with the oxygen to form
carbon dioxide and carbon monoxide, which provides heat for the
subsequent gasification reactions. According to certain
embodiments, temperatures during the combustion process may range
from approximately 700.degree. C. to 1600.degree. C. Next, steam
may be introduced into the gasifier 20 during a gasification step.
The char may react with the carbon dioxide and steam to produce
carbon monoxide and hydrogen at temperatures ranging from
approximately 800.degree. C. to 1100.degree. C. In essence, the
gasifier 20 utilizes steam and oxygen to allow some of the
feedstock to be "burned" to produce carbon dioxide and energy,
which drives a second reaction that converts further feedstock to
additional hydrogen and carbon monoxide. In this way, a resultant
gas is manufactured by the gasifier 20. This resultant gas may
principally include carbon monoxide and hydrogen, as well as
methane, carbon dioxide, water, hydrogen chloride, hydrogen
fluoride, ammonia, hydrogen cyanide, and hydrogen sulfide and
carbonyl sulfide (depending on the sulfur content of the
feedstock). Non-gasifiable ash material and unconverted and/or
incompletely converted fuel from the feedstock slurry may be
byproducts of the process that may exist as larger particles of
molten slag and smaller particles, referred to as fines or fine
slag.
[0022] From the reaction portion 24, the syngas may enter the
quench portion 26 where the syngas may be cooled and saturated. The
quench portion 26 may be an integral part of the gasifier 20 as
shown, or the quench portion 26 may be a separate unit. The quench
portion 26 may cool the syngas to at or near a saturation
temperature through evaporation of a cooling fluid, such as water,
causing less desirable components to solidify. In particular, the
molten slag may be rapidly cooled and solidified into coarse slag
particles 28 that may be collected in the bottom of the quench
portion 26.
[0023] In certain embodiments, the syngas and particulate solids
may undergo certain process steps after exiting gasifier 20 and
before entering quench portion 26. By way of non-limiting example,
these other processes may include, but are not limited to, partial
cooling by indirect heat exchange with boiler feed water to produce
steam. Additionally or alternatively, such processing may include
at least a partial separation of the slag and other particulate
solids from the syngas, and separately quenching the at least
partially separated slag and other particulate solids from the
syngas and remaining particulate solids, where the quenching of the
syngas and remaining particulate solids may include quenching,
cooling, or scrubbing, or any combination thereof, of the syngas
and remaining particulate solids in a scrubber to produce a stream
of saturated syngas and a stream of black water. Furthermore, the
syngas and particulates produced within the gasifier 20 may be used
as reactants to help convert additional feedstock in a second stage
reactor, may be contacted with steam or CO.sub.2 to modify the
composition of the syngas and/or partially cool the syngas and
particulate solids, and so on.
[0024] The coarse slag 28 may flow, for example, by gravity, from
the quench portion 26 into a pressurized lock hopper 30 at regular
intervals. For example, in some embodiments, a control valve 32 may
control the amount of coarse slag 28 delivered to the lock hopper
30. In certain embodiments, liquid 34 (e.g., water) may be removed
from the coarse slag 28 within the lock hopper 30 and returned to
the quench portion 26 of gasifier 20. In the illustrated
embodiment, the liquid 34 is motivated by a pump 36 disposed along
a divergent flow path 38 between the lock hopper 30 and the
gasifier 20. A resulting slag 29 may then be removed from the lock
hopper 30 and directed to a slag sump unit 40. For example, the
slag 29 is directed from the lock hopper 30, through a control
valve 42 and to the slag sump unit 40. The slag 29 settles to the
bottom of sump unit 40 and may be removed from the slag sump unit
40 using, for example, a slag drag conveyor (not shown), which
produces partially dewatered slag stream 43. Removal of slag stream
43 facilitates recovery of the water remaining in slag sump 40,
such as by use of sump pump 68, which produces a stream of slag
sump water 66. Indeed, in accordance with present embodiments, the
stream of slag sump water 66 is deaerated to eventually produce
grey water or process water that may be used for various processes
within the gasification system 10.
[0025] Returning to the operation of the gasifier 20, in addition
to producing slag 28, the quench portion 26 may produce partially
cooled syngas 42 and black water 44, which may also be referred to
as gasifier blowdown. The black water 44 includes a mixture of
fines and char, and water produced within the gasifier 20, and
generally will be at elevated temperatures, up to the saturation
temperature of the water at the pressure in quench 26. The
partially cooled syngas 42 may be directed to a syngas scrubbing
and treatment system 46 where additional fines, char and other
entrained gases, such as hydrogen chloride, may be removed. In
particular, within the syngas scrubbing and treatment system 46,
the fines and char may be separated from the syngas to produce
another stream of black water 48 that may exit a bottom portion of
the syngas scrubbing and treatment system 46 while scrubbed syngas
50 may exit the syngas scrubbing and treatment system 46.
[0026] The black water 48 exiting the syngas scrubbing and
treatment system 46 may be used in quench portion 26, or may be
combined with the black water 44 from the quench portion 26 and be
directed to a black water processing system 52. In other
embodiments, the black water 44 and the black water 48 may be
provided to the black water processing system 52 as separate
streams. The black water processing system 52 may include one or
more flash tanks that subject the black water 44 and 48 to a series
of pressure reductions to remove dissolved gases and concentrate
the fines. Heat from the flash tanks may be recovered and used to
heat other streams within the gasification system 10.
[0027] The black water processing system 52 of FIG. 1 includes a
high pressure flash tank 54, a low pressure flash tank 56, and a
settler 58. Although the high and low pressure flash tanks 54, 56
are illustrated, in other embodiments, the gasification system 10
may include only the low pressure flash tank 56, as discussed
below. The high and low pressure flash tanks 54, 56, in a general
sense, may promote separation of fines through a reduction in
pressure that causes the black water 44 to be partially evaporated
and cooled. In the illustrated embodiment, the high and low
pressure flash tanks 54, 56 subject the black water 44 to a
progressively reduced pressure, thereby facilitating further
removal of dissolved gases. According to certain embodiments, the
dissolved gases may include syngas, absorbed from quench portion 26
and/or syngas scrubbing and treatment system 46.
[0028] During operation, the black water 44 is discharged from the
quench portion 26 of the gasifier 20, and flows through a level
control valve 60. The level control valve 60 may control the liquid
level in high-pressure flash tank 54, and consequently the amount
of black water 44 flowing to the high-pressure flash tank 54.
Control valve 60 also may partially flash the black water 44 to
produce steam in addition to any steam that may already be present
in the black water 44. For example, the level control valve 60 may
reduce the pressure of the black water 44 to between approximately
20.7 bar (300 pound per square inch (PSI)) and approximately 62.1
bar (900 PSI), such as between approximately 25 bar and 55 bar, 30
bar and 45 bar, or 35 bar and 40 bar.
[0029] The high-pressure flash tank 54 is configured to perform a
first flash event on the black water 44 to produce a first overhead
vapor 62. Indeed, the high pressure flash tank 54 may flash the
black water 44 to a first reduced pressure, such as to between
approximately 20.7 bar-gauge (barg) (approximately 300 PSI-gauge
(PSIG)) and approximately 6.9 barg (approximately 100 PSIG). For
example, the pressure of the black water 44 may be reduced to
between approximately 20 barg and 7 barg, such as between
approximately 18 barg and 9 barg, 16 barg and 11 barg, or 14 barg
and 13 barg. The first overhead vapor 62 produced by the first
flash event may include a mixture of syngas, hydrogen (H.sub.2),
CO, CO.sub.2, and hydrogen sulfide (H.sub.2S). The first overhead
vapor 62 may be provided to the syngas scrubbing and treatment
system 46 where various gas separation and capture processes are
performed.
[0030] The pressure within the high pressure flash vessel 54 and,
thus, the extent to which the black water 44 is flashed, is
controlled using a pressure control valve 63. For example, the
pressure control valve 63 may control the backpressure of the first
overhead vapor 62 by controlling its flow rate to downstream
processes. That is, as the flow of the first overhead vapor 62 is
adjusted by the pressure control valve 63, the pressure within the
high pressure flash vessel 54 also adjusts.
[0031] In addition, the high pressure flash tank 54 produces a
first discharged black water 64 that exits proximate a lower
portion (e.g., the bottom) of the high pressure flash tank 54. The
first discharged black water 64 may be cooled compared to the
blackwater 44 produced at the quench portion 26 of the gasifier 20.
For example, as the first overhead vapor 62 begins to evaporate
away from the bulk of the black water 44, the black water within
the high-pressure flash tank 54 may cool. For example, the black
water 44 may be between 215 and 270.degree. C., such as between 230
and 250.degree. C., while after cooling the first discharged stream
black water 64 may have cooled to between 170 and 220.degree. C.,
such as between 185 and 210.degree. C.
[0032] Once the first discharged black water 64 is produced, it is
provided to the low-pressure flash tank 56. In the illustrated
embodiment, the first discharged black water 64 is provided to a
lower portion of the low-pressure flash tank 56 (e.g., proximate
the bottom of the low pressure flash tank 56). Indeed, in
accordance with present embodiments, vapor produced by flashing the
first discharged black water 64 within the low-pressure flash tank
56 may be used as a first flash gas within the low-pressure flash
tank 56, as is described in detail below.
[0033] Substantially simultaneously, a stream of sump water 66 is
provided to the low-pressure flash tank 56 at an upper portion
(e.g., proximate the top of the low pressure flash tank 56). For
example, as illustrated, the stream of sump water 66 is motivated
toward the low-pressure flash tank 56 by a sump pump 68. In
accordance with certain embodiments, the stream of sump water 66
may include dissolved oxygen from atmospheric air proximate the
slag sump 40, and may have a lower temperature than the black water
44 and the first discharged black water 64. Unfortunately, the
dissolved oxygen may preclude the use of this sump water in other
plant processes, as the oxygen may oxidize and corrode various
conduits, vessels, and other plant equipment. However, the present
embodiments provide for the stream of sump water 66 to be contacted
with vapor produced from the first discharged black water 64 within
the low-pressure flash tank 56 in a manner that deaerates the
stream of sump water 66 and cools the vapor.
[0034] For example, as is discussed in detail below with respect to
FIGS. 3-5, the low-pressure flash tank 56 includes one or more
gas-liquid contacting features for contacting a flash gas produced
from the first discharged black water 64 with the stream of slag
sump water 66. Indeed, the amount of first discharged black water
64 that may be provided to the low-pressure flash tank 56 may be at
least partially controlled using a level control valve 70 disposed
along a conduit 72 fluidly coupling the high-pressure flash tank 54
and the low-pressure flash tank 56. The level control valve 70, in
addition to controlling the level in high-pressure flash tank 54
and therefore the flow of the first discharged black water 64 along
the conduit 72, may also partially flash the first discharged black
water 64 to produce at least a portion of the flash gas that will
be used to deaerate the stream of sump water 66. Indeed, level
control valve 70 may reduce the pressure of the first discharged
black water 64 to between approximately 4.8 bar (70 PSI) and
approximately 17.2 bar (250 PSI), such as between approximately 5.0
bar and 17.0 bar, 7.0 bar and 15.0 bar, or 9.0 bar and 11.0 bar.
Accordingly, as the first discharged black water 64 enters the
low-pressure flash tank 56, the first discharged black water 64 may
be a multi-phase flow (e.g., a three-phase flow) including vapor
such as steam, some CO.sub.2, some syngas, and various particulates
(e.g., fines and char).
[0035] The low-pressure flash tank 56 has a reduced internal
pressure compared to the pressure in the high-pressure flash tank
54. As an example, the low-pressure flash tank 56 may reduce the
pressure of the incoming first discharged black water 64 to between
approximately 1.4 and 3.4 barg to produce a flash gas. For example,
pressure of the first discharged black water 64 may be reduced to
between approximately 2.2 and 3.1 barg, or 2.5 and 2.9 barg.
Indeed, as this pressure reduction occurs, the first discharged
black water 64 produces the flash gas or vapor, which flows toward
the top of the low-pressure flash tank 56. Because the stream of
slag sump water 66 enters the top of the low-pressure flash tank
56, and is substantially in the liquid phase, it begins to flow
down toward the bottom of the low-pressure flash tank 56. The
combination of the countercurrent flow of the stream of slag sump
water 66 and the flash gas and the gas-liquid contacting features
within the low-pressure flash tank 56 causes the flash gas to strip
a substantial portion of the dissolved gases from within the stream
of slag sump water 66. This causes the stream of slag sump water 66
to become deaerated, while cooling the flash gas to produce a
second overhead vapor 74. As with the first overhead vapor 62, the
flow rate of the second overhead vapor 74 is controlled using a
pressure control valve 75. Thus, pressure control valve 75 also
controls the pressure within the low pressure flash vessel 56 and
the extent to which the first discharged black water 64 is
flashed.
[0036] In addition to the first discharged black water 64 and the
stream of slag sump water 66 that are provided to the low-pressure
flash tank 56, in some embodiments, a stream of low-pressure steam
76 may also be provided to the tank 56. For example, the
low-pressure steam 76 may help to regulate the pressure and/or
temperature within the low-pressure flash tank 56. The low-pressure
steam 76 may also help to flash the first discharged black water 64
as it enters the low-pressure flash tank 56. The low-pressure
stream 76 must be at a pressure at least as high as the pressure in
the low-pressure flash tank 56. Thus, in some embodiments, the
pressure of the low-pressure steam 76 may be between approximately
2 and 8 bar, such as between approximately 3 and 6 bar, or 4 and 5
bar. It should be noted that while the illustrated embodiment
depicts the low-pressure steam 76 as being provided to the
low-pressure flash tank 56, in some embodiments the low-pressure
steam 76 may not be provided.
[0037] As the first discharged black water 64 flashes within the
low-pressure flash tank 56, the produced flash gas deaerates the
stream of slag sump water 66 to produce the second overhead vapor
74 and a deaerated liquid discharge 77 having deaerated slag sump
water and a liquid portion (i.e., non-flashed portion) of the first
discharged black water 64. As noted above, the flashing process
results in cooling of the residual fluids left in the tank.
Moreover, because the stream of slag sump water 66 has a
temperature ranging between approximately 50 and 100.degree. C.,
such as between approximately 60 and 90.degree. C. or 70 and
80.degree. C., the second overhead vapor 74 has a reduced
temperature compared to the first discharged black water 64. For
example, the second overhead vapor 74 may have a temperature
between approximately 100 and 150.degree. C. For example, the
temperature may be between approximately 90 and 140.degree. C., 95
and 140.degree. C., or 100 and 130.degree. C. It should be noted
that the reduced temperature of the second overhead vapor 74 may
obviate the need for various additional cooling and treatment
features, which may otherwise be used when the stream of slag sump
water 66 is not contacted with flash gas produced from the first
discharged black water 64. Furthermore, such contacting may obviate
the need for additional deaeration features for the stream of slag
sump water 66, such as vacuum flash tanks, deaerators, and so on.
Thus, in addition to providing savings in equipment and operational
costs, the present embodiments may allow the deaerated liquid
discharge 77 to be directly processed by processing equipment, with
its constituents (e.g., water, fine slag) being used for various
purposes, such as make-up water, road base, and so on.
[0038] For example, in the illustrated embodiment, the deaerated
liquid discharge 77 exits the low-pressure flash tank 56, and is
directed to a heat exchanger 78 where it is cooled to below
approximately 100.degree. C. For example, the deaerated liquid
discharge 77 may be cooled to between approximately 40 and
100.degree. C., 50 and 90.degree. C., 60 and 80.degree. C., or to
approximately 77.degree. C. The cooled temperature of the deaerated
liquid discharge 77 may aid in the separation of constituent grey
water 80 and a concentrated fine slag and char stream 82 within the
settler 58. Indeed, the deaerated liquid discharge 77 may be
provided to the settler 58, and a substantial portion of the fine
slag and char within the discharge 77 may settle. This produces the
grey water 80 and the concentrated fine slag and char stream 82,
with the grey water 80 being sent for further purification, for use
as a source of make-up water, or for use in the gasification
reaction (e.g., as a quench water source for quench portion 26).
The concentrated fine slag and char stream 82 may be removed from a
bottom portion of the settler 58 and provided to a filter 84, such
as a rotary filter. For example, the concentrated fine slag and
char stream 82 may be pumped to the filter 84 by a pump 86, and the
concentrated fine slag and char stream 82 may be further separated
into a filter cake 88 and a filtrate stream 90. The filter cake 88
may include solid fine slag and other particulates that are
produced by the gasification reaction. The filtrate stream 90 may
include the water of the concentrated fine slag and char stream 82,
as well as fine particulates that are not removed by the filter
84.
[0039] It should be noted that filtrate stream 90 is recycled to
the slag sump 40. This filtrate stream 90 may constitute at least a
portion of the stream of slag sump water 66 that is provided to the
low pressure flash vessel 56. Alternatively, filtrate stream 90 may
be directly routed to low pressure flash vessel 56, which is
illustrated as alternate stream 91. Thus, the alternate stream 91
may enter into the low pressure flash vessel 56 via an inlet that
is the same as, or different than an inlet configured to receive
slag sump water 66. Indeed, in certain embodiments, stream 90 may
be routed separately from or instead of the slag sump water 66.
Moreover, at least one other water stream 93 for use in
gasification system 10 may be deaerated separately or in
combination with either or both the slag sump water 66 and the
fines filtrate stream 90 in low pressure flash vessel 56, including
but not limited to process water makeup. In other words, the low
pressure flash vessel 56 may also deaerate the filtrate stream 90
and the at least one other water stream 93 for use in the syngas
production system. Accordingly, the low pressure flash vessel 56
may include a respective inlet for steam 93, or stream 93 may be
introduced into the low pressure flash vessel 56 via the same
inlets used for either or both of the slag sump water 66 and/or the
alternate stream 91.
[0040] While it may be desirable to let the pressure of the black
water 44 (i.e., the gasifier blowdown) down over more than one
stage, the present embodiments also provide for the pressure and
temperature to be reduced in a single stage at the low-pressure
flash tank 56. Indeed, such embodiments may further reduce the
equipment and operational costs associated with the treatment of
blowdown water from the quench portion 26. FIG. 2 illustrates an
embodiment of such a black water treatment system 100 having only
one flash tank, such as a low-pressure flash tank, for treating
blowdown water (e.g., black water 44 and 48), which includes
byproducts from gasifier 20. Indeed, the black water treatment
system 100 is illustrated as a part of the gasification system 10.
Accordingly, the components of the black water treatment system 100
will be discussed in a similar context to the gasification process
described above with respect to FIG. 1 using the same reference
numerals for the same elements.
[0041] As described above, the gasifier 20 produces untreated
syngas 42, slag 28, and blackwater 44. The untreated syngas 42 is
provided to the syngas scrubbing and treatment system 46, which
produces scrubbed and treated syngas 50 and additional black water
48. The coarse slag 28 is provided to the lock hopper 30, which
sends the slag 29 to the slag sump 40, where the slag 29 remains
until the stream of slag sump water 66 is utilized in the black
water treatment system 100.
[0042] In the illustrated embodiment, the black water 44, which may
include the additional black water 48 produced at the syngas
scrubbing and treatment system 46, is provided directly to the
low-pressure flash tank 56 without the high-pressure flash tank 54.
Specifically, the black water 44 flows through a level control
valve 102 disposed along a conduit 104 fluidly coupling the
low-pressure flash tank 56 with the quench portion 26. The level
control valve 102 may flash the black water 44 to produce, in some
embodiments, a multi-phase flow including steam, some CO.sub.2,
some syngas, water, and slag particulates. For example, the level
control valve 102 may reduce the pressure of the black water 44 to
between approximately 24.1 bar (350 PSI) and approximately 80.7 bar
(1170 PSI), such as between approximately 30 bar and 75 bar, or 40
bar and 50 bar.
[0043] Because the black water 44 has not been flashed in a flash
tank prior to introduction into the low-pressure flash tank 56, the
black water entering the low-pressure flash tank 56 may have a
higher temperature than described above with respect to FIG. 1. For
example, the black water 44, upon or immediately prior to
introduction to the low-pressure flash tank 56, may have a
temperature of between approximately 215 and 270.degree. C., such
as between approximately 230 and 250.degree. C. As noted above, the
pressure of the low-pressure flash tank 56 may be between
approximately 1.4 and 3.4 barg, such as between approximately 2.2
and 3.1 barg, 2.5 or 2.9 barg. Indeed, because the black water 44
may have a much higher pressure before introduction into the
low-pressure flash tank 56, such as between approximately 20 and 80
barg, 30 and 70 barg, or 40 and 70 barg (e.g., 69 barg), the black
water 44 may flash upon entry into the low-pressure flash tank 56.
Indeed, in accordance with one embodiment, the black water 44
flashes to produce a first flash gas within the low-pressure flash
tank 56.
[0044] Substantially simultaneously, the stream of slag sump water
66 may be provided to the low-pressure flash tank 56, as noted
above. The pressure within the low-pressure flash tank 56 is such
that the first flash gas, which is a flashed portion of the black
water 44, deaerates the stream of slag sump water 66 as the two
flows mix via a countercurrent and via a gas-liquid contacting
feature. The gas-liquid contacting feature may include a plurality
of Raschig rings (e.g., hollow cylindrical structures), one or more
valve trays (e.g., fixed valve trays), or the like. The stream of
slag sump water 66, as noted above, also cools the first flash gas
and the remaining black water 44 within the low-pressure flash tank
56. Thus, as a result of this mixing, deaeration, and cooling, an
overhead vapor 106 and a deaerated liquid discharge 108 are
produced by the tank 56. The overhead vapor 106, which exits
proximate the top of the low-pressure flash tank 56, may therefore
include at least a substantial portion of the oxygen previously
dissolved in the stream of slag sump water 66, steam, some syngas,
some CO.sub.2, some acid gas, and similar gases. Moreover, the
overhead vapor 106 may have a pressure that is substantially equal
to the pressure within the low-pressure flash tank 56. Further, as
discussed above with respect to FIG. 1, the pressure within the low
pressure flash vessel 56 is controlled by a pressure control valve
107. The pressure control valve 107 controls the flow rate of the
overhead vapor 106 and, therefore, its backpressure, which adjusts
the extent to which the black water 44 is flashed within the low
pressure flash vessel 56.
[0045] As noted above, the black water 44, which in the illustrated
embodiment is provided directly to the low-pressure flash tank 56,
is utilized to deaerate the stream of slag sump water 66. Indeed,
in accordance with present embodiments, the first flash gas (i.e.,
the flashed portion of the black water 44 within the low-pressure
flash tank 56) may remove between 60 and 100% of the oxygen
dissolved within the stream of slag sump water 66. For example, the
first flash gas may remove between approximately 70 and 100%, 80
and 100%, or 90 and 100% of the dissolved oxygen. Indeed, in some
embodiments, the first flash gas may deaerate the stream of slag
sump water 66 to an extent such that any dissolved oxygen present
in the stream of slag sump water 66 may have little to no effect on
piping, conduits, pumps, or other vessels that the deaerated liquid
discharge 108 may contact during operation of the system 10.
[0046] The deaerated liquid discharge 108, in a similar manner to
the deaerated liquid discharge 77 of FIG. 1, is cooled in the heat
exchanger 78 and provided to the settler 58. The settler 58
produces grey water 80 and the concentrated fine slag and char
stream 82. The concentrated fine slag and char stream 82 is
provided to the filter 84, which separates the concentrated fine
slag and char stream 82 into the filter cake 88 for inclusion in
various solid materials (e.g., road base) and the fines filtrate
90, which is used as a source of make-up water for the slag sump
40. In some embodiments, the filter cake 88 may additionally or
alternatively be used in the gasifier 20 as a source of fuel. In
other embodiments the fines filtrate 90 may be used for feedstock
slurry preparation and/or as grey water makeup by feeding the fines
filtrate 90 to the low-pressure flash tank 56 for deaeration.
[0047] Moving now to FIG. 3, an embodiment of the low-pressure
flash tank 56 is illustrated as including a first inlet 120, a
second inlet 122 disposed below the first inlet 120, and a
gas-liquid contactor 124 disposed between the first inlet 120 and
the second inlet 122. The first inlet 120 is configured to receive
a stream of slag sump water 126 (e.g., from the slag sump 40 of
FIGS. 1 and 2) at an upper portion 128 of the low-pressure flash
tank 56. Conversely, the second inlet 122 is configured to receive
a gasifier blowdown 130 at a lower portion 132 of the low-pressure
flash tank 56. As an example, the gasifier blowdown 130 may include
the stream of black water 44 of FIG. 2 or the first discharged
black water 64 of FIG. 1. Accordingly, the gas-liquid contactor 124
is positioned to facilitate the mixing of the slag sump water 126
as it falls downward within the low-pressure flash tank 56 with the
upward-rising flash gas produced from the gasifier blowdown 130 as
it flashes within the low-pressure flash tank 56.
[0048] The low-pressure flash tank 56 also includes a third inlet
134 configured to receive the low-pressure steam 76, which may
facilitate pressure and/or temperature maintenance within the
low-pressure flash vessel 56 and/or facilitate the flashing of the
gasifier blowdown 130. A liquid 136, such as water or a mixture of
water and other gasification products, is also present within the
low-pressure flash tank 56 during operation. In accordance with
present embodiments, the liquid 136 includes various black water
components and slag sump water components, including slag and char,
which may be residual from the gasifier blowdown 130 and the slag
sump water 126. The liquid 136 may also include other dissolved
gases at reduced concentrations compared to liquid water feeds 126
and 130, such as a small amount of syngas, inert gases, acid gases,
among others, but may generally be considered to be deaerated, as
is discussed below.
[0049] A level 138 of the liquid 136 may be controlled using a
level control 140, which is operatively connected to the
low-pressure flash tank 56 and to a flow control valve 142 disposed
along a conduit 144 leading from the low-pressure flash tank 56 to
a cooling/settling area 146. The cooling/settling area 146, in some
embodiments, corresponds to the heat exchanger 78 and the settler
58, which lead to various filtration and water-recycling features
of the gasification system 10 of FIG. 1 or 2. Thus, the level
control 140, during operation, may monitor the level 138 of the
liquid 136 to determine appropriate rates at which to deliver a
deaerated liquid discharge (e.g., a portion of the liquid 136) from
the low-pressure flash vessel 56 to the cooling/settling area 146.
For example, the level control 140 may send control signals to an
actuator 148 of the flow control valve 142 to adjust the position
of the valve 142. As discussed in detail below, the pressure within
the low pressure flash vessel 56 is controlled by controlling the
flow of an overhead discharge from the vessel 56.
[0050] In addition to the features described above, the
low-pressure flash tank 56 also includes a trough 150 and a baffle
152 disposed proximate the first and second inlets 120, 122,
respectively. The trough 150 and the baffle 152, in a general
sense, are configured to enhance the contacting of the liquid
(e.g., the slag sump water 126) and the gas (e.g., the flashed
portion of the gasifier blowdown 130) by providing a substantially
even distribution of each across the low-pressure flash tank 56.
The trough 150 is configured to receive a downward flow 154
(illustrated as an arrow) of the slag sump water 126 within the
low-pressure flash tank 56. The trough 150 includes a base 156 with
a plurality of recesses 158 disposed in the base 156. The base 156
is configured to receive the flow 154 and distribute the flow 154
across the recesses 158 to form a plurality of streams 160,
illustrated as arrows. During operation, the streams 160 fall
downward toward the gas-liquid contactor 124. It should be noted
that while the low-pressure flash tank 56 is illustrated generally
as including the trough 150, in certain embodiments the flash tank
56 may not include a trough, such as when the gas-liquid contactor
124 includes fixed valve trays.
[0051] The baffle 152 includes a fixed or movable projection
disposed proximate the second inlet 122. The baffle 152 is
configured to impede the flow of the gasifier blowdown 130 into the
low-pressure flash tank 56. For example, impeding the flow of the
gasifier blowdown 130 within the low-pressure flash tank 56 may
prevent the influx of the blowdown 130 from impinging on an
upward-rising, first flash gas 162. Indeed, in certain embodiments,
reducing the impingement of the flow of the first flash gas 162 may
help maintain the rate at which the slag sump water 126 is
deaerated.
[0052] The first flash gas 162 may include a portion of the
gasifier blowdown 130 that has been flashed and, in some
embodiments, at least a portion of the low-pressure steam 76. In
some embodiments, the first flash gas 162 mainly includes
low-pressure steam produced from the blowdown 130 with trace gases
produced in the gasification process. As illustrated, during
operation, the first flash gas 162 and the streams 160 of the slag
sump 126 are directed to the gas liquid contactor 124, where the
slag sump 126 is deaerated while cooling the first flash gas
162.
[0053] The gas-liquid contactor 124, as noted above, is configured
to facilitate the contacting of the flash gas 162 and the streams
160. Generally, the gas-liquid contactor 124 includes features,
such as a plurality of flow impeding structures, to enable the
flash gas 162 and the streams 160 to pass through a confined area
to increase a probability of contacting via a counterflow. For
example, the gas-liquid contactor 124 may provide an increased
surface area for the streams 160 and the first flash gas 162 to
interact. Because the first flash gas 162 is at a higher
temperature than the streams 160, a certain amount of heat transfer
from the first flash gas 162 to the streams 160 occurs.
Accordingly, the first flash gas 162 is cooled while the streams
160 are heated. The increase in temperature of the streams 160 may
serve to drive the dissolved oxygen in the streams 160 out of
solution. Moreover, the first flash gas 162, being substantially
vapor, may entrain a substantial portion of the oxygen. For
example, the first flash gas 162 may entrain between 10 and 100% of
the oxygen within the streams 160, such as between approximately 20
and 100%, 30 and 100%, 40 and 100%, 50 and 99%, 60 and 95%, or 70
and 90% of the oxygen within the streams 160. Indeed, in accordance
with certain embodiments, the streams 160 may be deaerated by the
flash gas 162 such that greater than approximately 50%, 60%, 70%,
80%, 90%, or 95% of the oxygen is removed to produce a deaerated
slag sump water 164.
[0054] During operation, once the first flash gas 162 and the
streams 160 have interacted at the gas-liquid contactor 124, the
resulting deaerated slag sump water 164 may fall toward the bottom
portion 132 of the low-pressure flash tank 56 to become a part of
the liquid 136. The first flash gas 162, on the other hand, after
interacting with the streams 160, becomes a second flash gas 166
(illustrated as arrows) having an increased concentration of oxygen
and a reduced temperature compared to the first flash gas 162. The
second flash gas 166 exits a gas outlet 168 disposed at the upper
portion 128 of the low-pressure flash tank 56 as overhead vapor
170. The overhead vapor 170, which may correspond to the overhead
vapor 106 of FIG. 2 or the second overhead vapor 74 of FIG. 1, may
be provided to various features of the gasification system or other
plant features for heating, cooling, or for use as a combustion
fuel.
[0055] The pressure within the low-pressure flash tank 56 may be
adjusted by controlling a backpressure of the overhead vapor 170,
such as by using a backpressure control 172. The backpressure
control 172 is operatively connected to the low-pressure flash tank
56 and an actuator 174 of a pressure control valve 176, which is
disposed along a conduit 178 leading from the low-pressure flash
tank 56 to various features of the gasification system or other
plant features for heating, cooling, or for use as a combustion
fuel. The backpressure control 172, during operation, may monitor
the backpressure of the overhead vapor 170 and/or the pressure
within the low pressure flash vessel 56 to determine appropriate
rates at which to discharge the overhead vapor 170. For example,
the backpressure control 172 may send control signals to the
actuator 174 of the pressure control valve 176 to adjust the
position of the valve 176 and, therefore, the flow rate of the
overhead vapor 170 through the conduit 178.
[0056] It should be noted that the composition of the liquid 136
and the overhead vapor 170 may depend, at least partially, on the
type of gas-liquid contactor 124 that is used in the tank 56. For
example, the amount of deaeration that the first flash gas 162
performs on the slag sump 126 may depend on the manner in which the
two are contacted. Indeed, the gas-liquid contactor 124 may include
one or more valve trays, a sieve tray, a packed bed, a cap tray, or
any feature capable of impeding flow and/or increasing the surface
area between the first flash gas 162 and the slag sump 126. In
embodiments in which the gas-liquid contactor 124 includes one or
more valve trays, the valve trays may be fixed valve trays as
opposed to movable valve trays. For example, fixed valve trays may
enable a substantially constant flow of the slag sump water 126
through the gas-liquid contactor 124, unlike movable valve trays,
which may become clogged by slag or other particulates. Similarly,
in embodiments where the gas-liquid contactor 124 includes a sieve
tray or a packed bed, the packed bed or the sieve tray may be
configured such that filtration of the slag or other particulates
is avoided, as the particulates may eventually cake and impede the
flow of the slag sump water 126 through the gas-liquid contactor
124. For example, in embodiments where the gas-liquid contactor 124
includes a packed bed of Raschig rings, the Raschig rings may have
openings that are larger than the slag particulates of the slag
sump water 126 to avoid filtration of the slag sump water 126 and
clogging of the packed bed.
[0057] One embodiment of the low-pressure flash tank 56 where the
gas-liquid contactor 124 includes a plurality of fixed valve trays
180 is illustrated schematically in FIG. 4. While the embodiment
illustrated in FIG. 4 includes three fixed valve trays, it should
be noted that the low-pressure flash tank 56 may include any number
of fixed valve trays to facilitate the removal of oxygen from the
slag sump water 126. However, it should be noted that as the number
of fixed valve trays increases, the cooling of the flash gas may
also increase, which may increase the probability of condensing
certain portions of the flash gas, such as the steam components.
Accordingly, in some embodiments, the low-pressure flash vessel 56
may include from 1 to 5 fixed valve trays, from 1 to 4, or from 1
to 3 fixed valve trays.
[0058] As illustrated, the low-pressure flash tank 56 includes a
first fixed valve tray 182, a second fixed valve tray 184, and a
third fixed valve tray 186. Each of the fixed valve trays 182, 184,
186 includes a main tray portion 188 and a plurality of fixed
valves 190, which are each projections covering holes in the main
tray portion 188. During operation, the upward-rising flash gases
162 pass through the valves 190 toward the upper portion 128 of the
low-pressure flash tank 56 while the downward flow 154 of the slag
sump water 126 flows over the trays 182, 184, 186 and generally
downward toward the bottom portion 132. Specifically, the slag sump
water 126 flows across the trays 182, 184, 186 as the flash gases
162 pass through the fixed valves 190. This allows the flash gases
to interact with the slag sump water 126 at least at the valves
190. The slag sump water 126 flows to downcomers 193 at the end of
each tray 182, 184, 186, which enables the slag sump water 126 to
flow down across the next tray, or to the liquid 136.
[0059] The fixed valve trays 182, 184, 186 may be spaced apart by a
distance 192 that facilitates flow as well as contacting between
the downward flow 154 of the slag sump water 126 and the flash
gases (e.g., the first flash gas 162). The spacing between the
trays may be approximately 24 inches (610 mm) A larger spacing,
such as 30 inches (760 mm), may also be used to provide more access
space between the trays. It may be appreciated that as the slag
sump water 126 flows down through or across the fixed valve trays
182, 184, 186, it may become increasingly deaerated. Similarly, as
the first flash gas 162 passes upward through the fixed valve trays
182, 184, 186, it may entrain increasing amounts of oxygen and may
be progressively cooled.
[0060] For example, with respect to the progressive deaeration of
the slag sump water 126, the flow 154 of the slag sump water 126,
upon entry into the tank 56, encounters the first fixed valve tray
182. As the flow 154 flows across the first fixed valve tray 182, a
first portion of the oxygen within the flow 154 of the slag sump
water 126 is removed by flash gas to produce a second flow 194
(illustrated as an arrow) of the slag sump water 126. Similarly, as
the second flow 194 encounters the second fixed valve tray 184, a
second portion of oxygen may be removed from the second flow 194 by
flash gas to produce a third flow 196 (illustrated as an arrow) of
the slag sump water 126. As the third flow 196 encounters the third
fixed valve tray 186, it is deaerated by the first flash gas 162 to
produce the deaerated slag sump water 164. As an example, the first
flash gas 162 may deaerate the third downward flow 196 of the slag
sump 126 such that between approximately 70 and 100%, 80 and 100%,
or 90 and 100% of the total dissolved oxygen of the slag sump water
126 has been removed within the low-pressure flash tank 56.
[0061] Regarding the progressive aeration and cooling of the first
flash gas 162, the process may be considered in an opposite context
to that described above for the downward flow 154 of the slag sump
water 126. Thus, the first flash gas 162 is cooled to a first
temperature to produce a first cooled flash gas 198 (illustrated as
an arrow). The first cooled flash gas 198, having a lower
temperature and a higher oxygen content compared to the first flash
gas 162 is further cooled by contact with the liquid flow on the
second tray 184, and entrains a second portion of oxygen to produce
a second cooled flash gas 200. The second cooled flash gas 200 is
further cooled by the flow 154 of the slag sump water 126 and
entrains a third portion of oxygen from the slag sump water 126 to
produce the second flash gas 166, which exits the low-pressure
flash tank 56 at the gas outlet 168 as the overhead vapor 170. As
an example, the second flash gas 166 may exit the low-pressure
flash tank 56 at a temperature of between approximately 90.degree.
C. and 150.degree. C., such as between approximately 90 and
140.degree. C., 95 and 130.degree. C., or 100 and 120.degree.
C.
[0062] While the embodiment of the low-pressure flash tank 56
described above facilitates the deaeration of the slag sump water
126 using fixed valve trays, as noted above, the gas-liquid
contactor 124 of FIG. 3 may include other features for contacting
the slag sump water 126 and the first flash gas 162. FIG. 5
illustrates an embodiment of the low-pressure flash tank 56 in
which the gas-liquid contactor 124 includes a plurality of Raschig
rings 210 formed into a packed bed 212. In a general sense, the
operation of the low-pressure flash tank 56 is the same as that
described above with respect to FIG. 3.
[0063] In the illustrated embodiment, the Raschig rings 210 include
hollow cylinders or similar hollow structures packed into the bed
212 in a random fashion. The Raschig rings 210 have a substantially
random orientation within the packed bed 212. Therefore, during
operation of the low-pressure flash tank 56, the first flash gas
162 and the streams 160 contact each other within the hollow
portion of the Raschig rings 210 and/or in the small spaces between
the Raschig rings 210. In certain embodiments, increasing the
contact area between the slag sump 126 and the first flash gas 162
may enhance the deaeration of the slag sump 126 and the cooling of
the first flash gas 162 compared to unconfined mixing via
countercurrent flow.
[0064] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
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